R1:5dec03af323f

Make OAuth scope handling more flexible

Summary:
Ref T7303. Currently, our handling of "scope" is fairly rigid and adheres to the spec, but some of these behaviors don't make much sense in practice.

Soften some behaviors and make them more flexible:

**Soft Failure on Unknown Permissions**: If a client asks for a permission we don't know about, just warn that we don't recognize it instead of fataling. In particular, I plan to make `offline_access` and `whoami` implicit. Older clients that request these…